Образуйте множественное число существительных 1. burglary 2. key 3.knife 4. knowledge 5. air 6. army 7.formula 8.child 9.wife 10.bottle 11.guitar 12.cloth 13.mouse 14.tooth 15.tomato 16.video 17.sheep 18.fruit 19.plan 20.tie 21. house 22.glass 23.fruit 24.path25.cigarette 26.bed27.cat 28.snow 29.holiday 30.cheese 31/vertebra 32. boy 33.child

1. burglary - burglaries
2. key - keys
3. knife - knives 
4. knowledge - uncountable  
5. air - uncountable (but if we talk about smb's manners, the plural form ("airs") is used; the sense, however, is absolutely different) 
6. army - armies
7. formula - formulas / formulae 
8. child - children
9. wife - wives
10. bottle - bottles
11. guitar - guitars
12. cloth - cloths (not to be confused with "clothes"!)
13. mouse - mice
14. tooth - teeth
15. tomato - tomatoes
16.video - videos 
17. sheep - sheep
18. fruit - fruits (when we talk about the successful results of our work; the plural form is also used in specialised literature) or uncountable (more often)
19. plan - plans
20. tie - ties
21. house - houses
22. glass - glasses or uncountable (if we talk about the substance) 
23. fruit - see above (№18)
24. path - paths
25. cigarette - cigarettes
26. bed - beds (countable, if we don't take some fixed expressions into account)
27. cat - cats 
28. snow - uncountable in most cases; I don't want to burden your memory with too many details, I don't think it necessary to explain when it can be countable :) 
29. holiday - holidays 
30. cheese - uncountable or countable ("cheeses") (when we talk about different types of this food) 
31. vertebra - vertebrae
32. boy - boys
33. child - children